Organised-crime investigation into American polygamous sect

America's most notorious polygamous sect is being investigated as an organised-crime operation, it emerged yesterday, in one of several signs that the net is closing on the group's fugitive leader.

Warren Jeffs, the self-declared prophet of the Fundamentalist Church of Jesus Christ of Latter-Day Saints, joined Osama bin Laden on the FBI's most-wanted list at the weekend, and the reward for information leading to his arrest was raised to $100,000 (£535,000). His case has featured on the high-profile television show America's Most Wanted, a Crimewatch-style programme that has led to many successful arrests in the past.

Mr Jeffs is wanted in Utah and Arizona on charges of sexual conduct with a minor and arranging bigamous marriages involving underage girls. The FBI describes him as "armed and dangerous".

Utah's attorney general, Mark Shurtleff, said he believed Mr Jeffs ran his church and its business arm, the United Effort Plan - reportedly worth $110m, as "an organised crime-type setup. We just have to get the evidence to prove it."

The church would be investigated for "double books, cooking books, offshore accounts and fraud", Mr Shurtleff told the Deseret Morning News, a Salt Lake City newspaper.

The church is one of several splinter groups that believes the Mormons should not have abandoned polygamy in the 19th century, a change made primarily so that Utah could be admitted to US statehood. Estimates of the number of Americans in polygamous marriages range from 20,000 to 100,000; the pro-polygamy group Principle Voices puts the figure at 37,000.

The practice has received a mixed portrayal in the American media. Jon Krakauer's best-selling 2003 book Under The Banner of Heaven focused on the prevalence of sex with underage girls and other exploitation. But a popular weekly television drama, Big Love, starring Bill Paxton as a man with "three wives and a thousand problems", treats its lead character broadly sympathetically.

Mr Jeffs inherited the sect from his father, and married all but two of his father's widowed wives. He has not been seen outside his community for two years, and is rumoured to move between the church's main premises in Utah and Arizona and its outposts in Texas, Colorado, South Dakota, Nevada, and British Columbia in Canada.